1. Field of the Invention
This invention relates to a dual intermittent microflame system for discrete point soldering and more particularly to a dual intermittent microflame system for discrete point soldering including a positive flow purge system to prevent flashback of combustible gas and oxygen.
2. Description of the Prior Art
Microflame soldering is well-known in the art and the requirements and technology therefore are disclosed in U.S. Pat. No. 5,169,053. In addition, see also U.S. Pat. Nos. 3,957,618; 4,113,601; 4,206,029; and 4,336,122. Generally speaking, many microflame systems such as illustrated in FIG. 1 include a generator which generates combustible gas which is delivered to a booster system for lowering the flame temperature, with the booster being connected to one or more torches. Most microflame soldering systems utilize a combustible gas mixture of hydrogen and oxygen. The mixture of hydrogen and oxygen will burn within the supply hoses if ignited. Normally, the flame at the nozzle tip does not ignite the combustible gas within the supply hoses because the combustible gas pressure is maintained by its supply, thereby preventing the flame from travelling back from the flame nozzle tip into the gas supply hose. Flashback is initiated from the flame nozzle tip when the external flame travels back into the gas supply hose when the gas pressure lowers as it exits the open flame nozzle tip.
The requirements in technology for high speed discrete point soldering, as disclosed in U.S. Pat. No. 5,169,053, have been established since the middle 1980s. The constraints of this technology have also been established with respect to cost, physical size and space required for the flame tip to swing into position, variability in heating and operator setup. With respect to cost, a conventional rotary microflame system generally consists of a gas supply, electrical gas valve, control system, flashback protection device, pneumatic rotary actuator, pneumatic pressure regulator, pneumatic flow controls, electronic pneumatic actuation valve, a pair of rotary travel stops, a pair of electrical rotary position sensors, timing belt drive, housing, rotary flame tip holder, and flame tip nozzle.
The physical size of the conventional rotary microflame housing is determined by the size of the rotary flame tip and is rotary actuated. The relatively large actuator size can prohibit access to some of the components to be soldered. In addition, other adjacent components are sometimes sensitive to the heat of the microflame as it is rotated into position to heat the parts to be soldered.
Heating of the parts to be soldered is affected by the actual time the flame is directed at the part. The pneumatic rotary actuator is affected by air pressure, air lubrication, pneumatic flow control, and the condition of the rotary actuator.
Control of the pneumatic rotary actuator of the prior art is critical because of the significant time it takes to apply heat to (400 milliseconds) and redirect heat (400 milliseconds) from the point to be soldered compared to the relatively short overall cycle time (900 milliseconds). With this rapid cycle time, the operator usually makes the corrections on a trial and test basis.
In the closed loop temperature based prior art systems, after the cycle is initiated, the gas valve is energized to feed gas to the nozzle tip, the electronic ignition creates a spark to the nozzle tip to ignite the gas, thereby causing a flame, the flame heats the part to the required temperature as determined by the temperature sensor, and the gas valve is then de-energized to shut off the flame.